Medical procedures are available for treatment of a variety of cardiovascular conditions, such as cardiac arrhythmias, atrial fibrillation, and other irregularities in the transmission of electrical impulses through the heart. As an alternative to open-heart surgery, many medical procedures are performed using minimally invasive surgical techniques, where one or more slender implements are inserted through one or more small incisions into a patient's body. Such procedures may involve the use of catheters or probes having multiple sensors, electrodes, or other measurement and treatment components to treat the diseased area of the heart, vasculature, or other tissue. Minimally-invasive devices are desirable for various medical and surgical applications because they allow for shorter patient recovery times compared to surgery, and for precise treatment of localized discrete tissues that are otherwise difficult to access. For example, catheters may be easily inserted and navigated through the blood vessels and arteries, allowing non-invasive access to areas of the body with relatively little trauma, while other minimally-invasive probes or instruments may be inserted into small openings and directed through targeted anatomy without significant impact or disruption to surrounding tissue.
One such example of a minimally invasive therapy involves the treatment of cardiac arrhythmias or irregular heartbeats in which physicians employ specialized cardiac assessment and treatment devices, such as a mapping and/or ablation catheter, to gain access to interior regions of a patient's body. Such devices may include tip electrodes or other ablating elements to create lesions or other anatomical effects that disrupt or block electrical pathways through the targeted tissue. In the treatment of cardiac arrhythmias, a specific area of cardiac tissue having aberrant electrical activity (e.g. focal trigger, slow conduction, excessively rapid repolarization, fractionated electrogram, etc.) is typically identified first before subsequent treatment. This localization or identification can include obtaining unipolar or bipolar electrograms, or monophasic action potential (“MAP”) electrograms of a particular cardiac region. Monophasic action potential recordings document the onset of local tissue depolarization, during repolarization, and the general action potential morphology. The MAP signal is generated by measurement between two electrodes, the first being in contact with the blood but generally not in contact with the myocardium, and the second being in contact with the myocardium, with high enough local pressure to depolarize the underlying myocytes. This increased local pressure preferably is created by a relatively prominent, yet small surface area electrode in stable contact with the myocardium.
MAP signals may be obtained by temporarily depolarizing selected tissue, with responsive electrical activity being recorded or otherwise monitored for an indication of local depolarization timing, refractory period duration, and any aberrant electrical activity. After mapping and diagnosing aberrant tissue, a physician may decide to treat the patient by ablating the tissue. Accurate mapping of the cardiac tissue using bipolar, unipolar, or MAP electrogram signals can reduce the number of ablations necessary to treat an aberrant electrical pathway, and can make the executed ablations more effective. In addition, MAP recordings can substantially improve the ability to determine the timing of local tissue activation which is often ambiguous when recorded using standard intracardiac electrodes.
The accuracy of MAP signal measurement largely depends on quality of contact between one or more mapping electrodes and the heart tissue. For example, motion artifacts caused by a beating heart and nonuniform ventricular contraction can significantly distort detected MAP signals, as movement of the heart will vary the pressure of (and therefore alter the contact between) the mapping electrodes on the heart tissue as well as resulting in unstable sliding contact of the electrodes. Currently known diagnostic cardiac electrophysiology catheters do not accurately and reliably detect MAP signals.
Further, combination mapping and ablation devices reduce procedure time and complexity by eliminating the need to employ separate mapping and ablation devices for each task. Combination mapping and ablation devices also increase ablation accuracy, because once aberrant tissue (the “target tissue”) is found, ablation can begin immediately without having to remove the mapping device and relocate the target tissue with the ablation device. It is desirable to include one or more larger electrodes for radiofrequency (RF) ablation, so the large electrode area can provide a large surface area for dissipation into the blood pool of heat absorbed from the tissues. When smaller electrodes, and therefore a smaller active surface area, are used, the electrodes are more likely to incur local overheating, which can lead to thermal denaturation of blood proteins, producing adherent or embolic coagulum or other undesirable effects downstream of the electrodes and the treatment site. Conversely, more accurate electrograms and MAP recordings may be obtained with smaller mapping electrodes.
To provide more effective and efficient medical treatments, it is thus desirable to optimize the apparatus and method of use to ensure more uniform contact between a mapping device and cardiac tissue when recording MAP signals. It is also desirable to have a catheter that can both record monophasic action potentials, and subsequently ablate the local tissue if desired. It is further desirable to provide a mapping apparatus that is simple and cost effective to manufacture.